A beam director for use in 3D printers, such as the one disclosed in U.S. Pat. No. 9,435,998, which is incorporated herein by reference, comprises a first mirror rotating about its longitudinal axis, with a reflective surface at an acute angle to the longitudinal axis. Accordingly, a beam transmitted along the longitudinal axis may be redirected onto a second mirror, and then to a work surface, which is typically perpendicular to the longitudinal axis.
The second mirror may take the form of a rotating flat mirror or a stationary arcuate mirror, which is used to reflect the beam along straight or arcuate paths on the work surface.
Lower case x, y and z denotes local beam coordinates:
In this application we define a lower case x, y and z coordinates system that is cartesian coordinates that are local to the beam. Lower case z denotes the direction of the beam while x and y denotes the beam size. Therefore, any reference to lower case x, y or z axis will be referring to local coordinates of the beam.
Upper case X, Y and Z denotes global system coordinates shown in FIGS. 2, 3, 4, 5, 6, 9 and 10.
With reference to FIG. 1, an embodiment of the aforementioned beam director includes a first reflector 106E, which is rotatable by an actuator 108 and which reflects the beam 107A onto a second conical reflector 131, which is based on a typical cone shaped segment. The reflective surface 132 of the second conical reflector 131 re-directs the beam 107A by about 90° onto a work surface. After the the beam 107A hits the conical reflector surface 132, the beam property will change as follows considering a collimated beam source 107A:
The beam will keep moving in the Z direction (90° shift); caused by the 45° cone.
When the source beam 3 is collimated, the beam x component 3B will no longer be parallel to the Z direction, as the cone curve will bring into focus the x component because of the rule of deflection as shown in FIG. 4.
The cone curve along the radius of 132 will add an optical diversion in the x axis that is proportional to the radius of the conical reflector 132. As an example, this will add a focal point proximate to the work surface in the x axis only, thus causing the departing beam 107A from the conical reflector 132 to have different focal point for x and for y. This is an undesired result: the desired result is either a collimated beam or a focusing beam in both x and y axis. To clarify; see FIG. 4, if beam 3 is a circular collimated beam with diameter D that is initially sent from a light source, the resulting beam output after the conical reflector 132 will have a distorted elliptic shape: Dx, the beam size in the x axis will be smaller than Dy, the beam size in the y axis, (11) before reaching the focal point and after reaching the focal point the x dimension of the beam 3B will be expending as the beam 3B continues to travel. The beam size components 11 are shown in FIG. 4 where the x component size is described by Dx and the y component by Dy respectfully.
Accordingly, an object of the present invention is to address the optical components for handling the beam of the prior art by providing corrective elements, whereby the beam has the same dimension in the first and second directions when incident on the work surface or when the beam keeps the proportion between the first and second directions when incident on the work surface.